Frost dates for W Glacier, MT
At W Glacier, the median last spring frost (32°F) is May 18 and the median first fall frost is Sep 20, for a typical growing season of 124 days. For a 90% chance that the last frost has passed, wait until Jun 4. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 18Last spring frost (median)50% chance of 32°F after this date
- Jun 4Safer planting date10% chance of 32°F after this date
- Sep 20First fall frost (median)50% chance of 32°F by this date
- 124 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 23 | Jun 8 | Jul 1 |
| 32°F | May 6 | May 18 | Jun 4 |
| 28°F | Apr 18 | May 1 | May 15 |
| 24°F | Mar 31 | Apr 14 | Apr 28 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 19 | Sep 4 | Sep 20 |
| 32°F | Sep 3 | Sep 20 | Oct 4 |
| 28°F | Sep 20 | Oct 4 | Oct 21 |
| 24°F | Oct 1 | Oct 19 | Nov 8 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 61 days | 85 days | 107 days |
| 32°F | 100 days | 124 days | 142 days |
| 28°F | 135 days | 155 days | 174 days |
| 24°F | 163 days | 186 days | 211 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59913 | 5a | -20 to -15°F | 8 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00248809, at 48.5003, -113.9847, elevation 960 m (3,148 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 180.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Hungry Horse Dam (18 km)
- Whitefish (29 km)
- Kalispell Glacier Airport (30 km)
- Creston (36 km)
- Polebridge (37 km)
- Olney (44 km)
- St. Mary 1 SSW (49 km)
- St. Mary (49 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.